Description:
A small 325mW amplifier with a voltage gain of 200 that can
be used as a bench amplifier, signal tracer or used to
amplify the output from personal radios, etc.
Notes:
The circuit is based on the National Semiconductor LM386
amplifier. In the diagram above, the LM386 forms a complete
non-inverting amplifier with voltage gain of x200.
A datasheet in PDF format can be downloaded from the
National Semiconductor website. The IC is available in
an 8 pin DIL package and several versions are available; the
LM386N-1 which has 325mW output into an 8 ohm load, the
Lm386N-3 which has 700mW output and the LM386N-4 which
offers 1000mW output. all versions work in this circuit.
The gain of the Lm386 can be controlled by the capacitor
across pins 1 and 8. With the 10u cap shown above, voltage
gain is 200, omitting this capacitor and the gain of the
amplifier is 20.
The IC works from 4 to 12Volts DC, 12Volt being the maximum
recommended value. The internal input impedance of the
amplifier is 50K, this is shunted with a 22k log
potentiometer so input impedance in this circuit will be
lower at about 15k. The input is DC coupled so care must be
taken not to amplify any DC from the preceding circuit,
otherwise the loudspeaker may be damaged. A coupling
capacitor may included in series with the 22k control to
prevent this from happening.
